Various dental materials are used for restorative treatment of teeth and examples thereof include inorganic materials and organic materials. Among the organic materials, polymerizable compositions containing a (meth)acrylic acid ester, a polymerization initiator, and a filler are widely used. The polymerizable compositions for restorative treatment of teeth can be broadly classified into two groups depending on their hardness obtained after curing. One of the groups consists of soft materials which are flexible when cured, and the soft materials are used, for example, in liners for denture bases, adhesive materials for oral cavity tissues such as temporary sealing materials, and shock-absorbing materials. The recent development of dentistry has created a need for a new soft material.
For example, it is common practice to attach a denture to a patient who has lost teeth for a cause such as aging. When a denture is used, a denture liner or a tissue conditioner is used in combination to improve the usability, such as to enable holding of the denture for a long time or reduce the shock to the jaw. Such a denture liner or tissue conditioner needs to have appropriate flexibility and shock-absorbing capacity.
Implantation has also become widely used for treatment of patients who have lost teeth for a cause such as aging. An implant is composed of an artificial tooth root to be embedded directly in the jawbone, a tooth crown placed above the artificial tooth root, and a tooth base, called an abutment, for connecting the artificial tooth root to the tooth crown. These parts are bonded together when used. This bonding is done with a temporary cement in some cases. The bonding portion needs to be removable since the implant must occasionally be retrieved for a maintenance process such as washing. A requirement for the temporary cement is therefore that its cured product should have appropriate flexibility. In the meantime, a tooth root of a living body includes a tissue called a periodontal membrane, and this tissue absorbs a biting-induced shock to reduce the transmission of the shock to the jawbone. However, a site treated with an implant lacks this periodontal membrane, and as such could permit shock transmission to the jawbone, which is why the artificial tooth root is required to reduce the biting-induced shock.
Addition of a flexible polymer is known as a method for imparting flexibility or shock-absorbing capacity to a cured product of a dental polymerizable composition. For example, Patent Literature 1 describes a polymerizable composition suitable for use in a temporary cement or a mobile tooth fixing material, the polymerizable composition containing an acrylic block copolymer added to improve the flexibility of a cured product of the composition. Patent Literature 2 describes a dental tissue conditioner to which is added an acrylic polymer powder having a glass transition temperature within a predetermined range. This dental tissue conditioner has the property of maintaining its original flexibility. Patent Literature 3 describes a dental adhesive containing a copolymer of a long-chain alkyl (meth)acrylate and a short-chain alkyl (meth)acrylate, the copolymer having a glass transition temperature within a predetermined range and a melting point within a predetermined range. This dental adhesive has good removability and adhesiveness. Patent Literature 4 describes a dental implant-protecting material in which a soft material is used, the protecting material having a loss tangent at 37° C. within a predetermined range. This dental implant-protecting material serves to dampen a biting-induced load on a fixture of an implant. That is, this dental implant-protecting material has good shock-reducing capacity. Patent Literature 5 describes a dental temporary cement composition containing a particular type of styrene block copolymer. This dental temporary cement has good adhesiveness suitable for temporary cementation to a metal or a ceramic.